Flowering in plants is a consequence of the transition of the shoot apex from vegetative to reproductive growth in response to environmental and internal signals. Currently, there is little information about how plants coordinate the activities of the cells that give rise to reproductive plant tissues, however, research has focused on identifying the genes that control this developmental process. Floral homeotic genes that control the specification of meristem and organ identity in developing flowers have been identified in Arabidopsis thaliana and Antirrhinum majus. Most of these genes belong to a large family of regulatory genes that possess a characteristic DNA binding domain known as the MADS-box. Members of this gene family display primarily floral-specific expression and are homologous to transcription factors found in several animal and fungal species. Molecular evolutionary analysis reveal that there are appreciable differences in the substitution rates between different domains of these plant MADS-box genes. Phylogenetic analysis also demonstrate that members of the plant MADS-box gene family are organized into several distinct gene groups: the AGAMOUS, APETALA3 (Ap3)/PISTILLATA and APETALA1/AGL9 groups. Several genes that belong to the APETALA3 (Ap3) group have been identified in Arabidopsis thaliana (Jack, et al., (1992) Cell 68:683-697). Genes of this group have been shown to play a role in the control of organ identity of petals and stamens during floral development (Bowman, et al., (1989) Plant Cell 1:37-52 and Bowman, et al., (1991) Development 112:1-20; Weigel and Meyerowitz (1994) Cell 78:203-209; Coen and Meyerowitz (1991) Nature 353:31-37; WO 93/21322). Thus, the shared evolutionary history of members of a gene group appear to reflect the distinct functional roles these MAD-box genes play in flower development.
The flowering locus T gene (FT) encodes a protein that appears to be involved in the regulating plant growth by controlling the rate at which maturation occurs. For example, an increase in FT function has been shown to produce early flowering (Kardailsky, et al., (1999) Science 286:1962-1965). Thus the FT gene may be useful to accelerate flowering in various crops.
The deduced sequence of the FT protein is similar to the sequence of TERMINAL FLOWER 1 (TFL1) and shares sequence similarity with membrane-associated mammalian proteins (Kardailsky, et al., (1999) Science 286:1962-1965). TFL1 in Arabidopsis, and the homologous Antirrhinum gene CENTRORADIALIS (CEN) play a key role in determining inflorescence architecture (Bradley, et al., (1997) Science 275:80-83; WO 97/10339; WO 99/53070).
FT protein belongs to a family of membrane-associated phosphatidylethanolamine-bind proteins (PEBP), which may function as kinase inhibitors to regulate the signal transudation pathways (Kardailsky, et al., (1999) Activation tagging of the floral inducer FT Science, December 3; 286 (5446); 1962-5. Also, Kobayashi, et al., (1999). A pair of related genes with antagonistic roles in mediating flowering signals Science December 3; 286 (5446); 1960-2.). The Arabidopsis gene TFL encodes a protein related to FT. Genes play antagonistic roles in the floral transition such as TFL is a repressor of flowering whereas FT is an activator (Kardailsky, et al., 1999; Kobayashi, et al., 1999). International patent application PCT/US01/43750 claims 9 corn homologs of the Arabidopsis FT. For continuity, maize genes were named ZmFT or ZmTFL (Table 1) accordingly to the degree of the translational homology to Arabidopsis FT-TFL proteins (GenBank accession numbers FT AB027504, TFL U77674).
There is a great deal of interest in identifying the genes that encode proteins involved in cellular differentiation in plants. These genes may be used in plant cells to control development. Accordingly, the availability of nucleic acid sequences encoding all or a portion of an Ap3 or FT or TFL1 gene homolog would facilitate studies to better understanding development in plants and provide genetic tools to enhance or otherwise alter plant developmental processes. Nucleic acid fragments encoding Ap3 homologs may be useful for engineering plant sterility/fertility, and flower development and morphology. Nucleic acid fragments encoding FT or TFL1 homologs may be useful for engineering flowering time, plant growth rate, inflorescence architecture, and tissue culture morphology and rate of cell division to enhance transformation.